In recent years, services using networks have become widespread. There is a growing demand for checking network quality status, and improving network facilities so that service users can comfortably use services. Therefore, as a technique for checking network quality status, there is a technique for estimating an available bandwidth at an IP (Internet Protocol) level by using a packet train composed of a series of measurement packets (Patent Document 1). In the technique of Patent Document 1, a plurality of measurement packets that monotonically increases or decreases, are sequentially transmitted from a transmission device at predetermined transmission intervals. Then, an available bandwidth is estimated in a receiving device, based on changes in reception intervals.